Biomedical subjects

S A Thomson

Publications and source records attributed to S A Thomson.

30 records · Page 2Linked to original sources

PubMed1994

NMR solution structure of a peptide nucleic acid complexed with RNA.

Peptide nucleic acids (PNA) incorporating nucleic acid bases into an achiral polyamide backbone bind to DNA in a sequence-dependent manner. The structure of a PNA-ribonucleic acid (RNA) complex was determined with nuclear magnetic resonance methods. A hexameric PNA formed a 1:1 complex with a complementary RNA that is an antiparallel, right-handed double helix with Watson-Crick base pairing similar to the "A" form structure of RNA duplexes. The achiral PNA backbone assumed a distinct conformation upon binding that differed from previously proposed models and provides a basis for further structure-based design of antisense agents.

Magnetic Resonance Spectroscopy↗

PubMed1994

The effects of histidine residue modification on the immune precipitating ability of rabbit IgG.

Treatment of anti-ovalbumin rabbit IgG with diethylpyrocarbonate (DEPC) at concentrations up to 100 microM led to a progressive decrease in the rates of formation of insoluble immune complexes, without affecting the final extent of immune complex formation. DEPC concentrations approximately 10-fold higher were needed to give comparable decreases in the rates of immune complex formation by F(ab')2. Treatment of DEPC-treated IgG with hydroxylamine led to substantial restoration of the rates of formation of insoluble immune complexes. Carbethoxylation of two histidine residues per IgG molecule had little effect on rates of formation of insoluble immune complexes, but these rates were markedly decreased in samples of IgG with four to five histidines per molecule modified. There were parallel decreases in the protein A-binding activity and in the rates of formation of insoluble immune complexes in IgG treated with increasing concentrations of DEPC. The presence of complement protein C1q restored the rates of formation of insoluble immune complexes of DEPC-treated IgG.

Animals↗

PubMed1993

Strand-invasion of duplex DNA by peptide nucleic acid oligomers.

Polyamide oligomers, termed peptide nucleic acids (PNAs), bind with high affinity to both DNA and RNA and offer both antisense and antigene approaches for regulating gene expression. When a PNA binds to a complementary sequence in a double-stranded DNA, one strand of the duplex is displaced, and a stable D-loop is formed. Unlike oligodeoxynucleotides for which binding polarity is determined by the deoxyribose sugar, the unrestrained polyamide backbone of the PNA could permit binding to a DNA target in an orientation-independent manner. We now provide evidence that PNAs can, in fact, bind to their complementary sequence in DNA independent of the DNA-strand polarity--that is, a PNA binds to DNA in both "parallel" and "antiparallel" fashion. With a mixed-sequence 15-mer PNA, kinetic studies of PNA.DNA interactions revealed that D-loop formation was rapid and the complex was stable for several hours. However, when measured either by gel-mobility-shift analysis or RNA polymerase II-elongation termination, D-loop formation was salt dependent, but PNA-strand dissociation was not salt dependent. We observed that D-loop-containing DNA fragments had anomalous gel mobilities that varied as a function of the position of the D-loop relative to the DNA termini. On the basis of permutation analysis, the decreased mobility of the PNA.DNA complex was attributed to a bend in the DNA at or near the D-loop.

Base Sequence↗

PubMed1993

Cystic fibrosis transmembrane conductance regulator splice variants are not conserved and fail to produce chloride channels.

In the human CFTR only the rare exon 4- splice variant is conserved in mice. We have discovered two novel murine variants, exon 5- and exon 11b+. The exon 5- variant represents up to 40% of mRNA in all CFTR-expressing tissues and leaves the reading frame intact. The exon 11b+ variant inserts a novel exon between exons 11 and 12 with expression restricted to the testis. Two variants of 11b have been found and both introduce premature stop codons. When we expressed human CFTR variants lacking either exon 5 or exon 9 in HeLa cells, they failed to generate cAMP-mediated chloride transport, due to defective intracellular processing. The lack of conservation of splice variants between species and the inability of the more abundant splice variants to generate protein that is correctly processed argue against a physiological role and may simply represent aberrant splicing that is tolerated by the cell and organism.

Alternative Splicing↗

PubMed1992

Antisense and antigene properties of peptide nucleic acids.

Peptide nucleic acids (PNAs) are polyamide oligomers that can strand invade duplex DNA, causing displacement of one DNA strand and formation of a D-loop. Binding of either a T10 PNA or a mixed sequence 15-mer PNA to the transcribed strand of a G-free transcription cassette caused 90 to 100 percent site-specific termination of pol II transcription elongation. When a T10 PNA was bound on the nontranscribed strand, site-specific inhibition never exceeded 50 percent. Binding of PNAs to RNA resulted in site-specific termination of both reverse transcription and in vitro translation, precisely at the position of the PNA.RNA heteroduplex. Nuclear microinjection of cells constitutively expressing SV40 large T antigen (T Ag) with either a 15-mer or 20-mer PNA targeted to the T Ag messenger RNA suppressed T Ag expression. This effect was specific in that there was no reduction in beta-galactosidase expression from a coinjected expression vector and no inhibition of T Ag expression after microinjection of a 10-mer PNA.

Animals↗

PubMed1988

Responses of rat alveolar macrophages to inhaled brass powder.

The effects of a single acute exposure to inhaled brass dust on rat pulmonary alveolar macrophages (PAM) were determined. Pulmonary alveolar macrophages lavaged from the lungs of these experimental animals showed both morphological and functional abnormalities. Exposure to brass dust caused a rapid, transient inflammatory response, producing an influx of polymorphonuclear leukocytes into the lavage fluid. Binucleation and multinucleation of PAM were sensitive morphological indicators of pulmonary stress that persisted throughout the 14-day course of the experiment. Pulmonary alveolar macrophages from rats exposed to brass dust were phagocytically activated; both the total numbers of test particulates ingested and the phagocytic index were elevated. Chemotaxis, as measured by direct cellular migration in Boyden chambers, was inhibited for 3 days after exposure, but was markedly stimulated from 7 to 14 days. This was interpreted as a possible consequence of a selective release of lymphokines during the course of the inflammatory response. Some of these results, based on in vivo exposure of PAM to inhaled particulates, differ from those derived from in vitro exposure. This points to the fact that it is virtually impossible to duplicate the native chemical microenvironment of PAM in vitro and emphasizes the necessity of bringing about PAM-particle interactions in the intact lung in order to obtain more physiologically relevant data.

Administration, Inhalation↗

PubMed1987

Dose of inhaled budesonide required to produce clinical suppression of plasma cortisol.

Increasing dose of budesonide, each dose given for a minimum of 1 month, were administered via a Nebuhaler to 14 patients. Two consecutive abnormally low fasting morning plasma cortisol values, taken 2 weeks apart, were accepted as evidence of hypothalamo-pituitary-adrenal (HPA) hypofunction. Data from nine of the 14 patients entering the study were available for analysis. One patient developed HPA hypofunction while inhaling 2.4 mg budesonide per day and another retained normal HPA function on a dose of 12 mg. In the remaining patients, intermediate doses resulted in suppression, or the patients were withdrawn unsuppressed for other reasons (n = 3). The results in this small patient sample suggest that budesonide administered via the Nebuhaler in doses up to 1.6 mg daily does not significantly affect plasma cortisol.

Administration, Inhalation↗

PubMed1986

Benzodiazepine-opiate antagonism--a problem in intensive-care therapy.

A 14-year-old previously fit schoolboy was admitted with staphylococcal pneumonia secondary to influenza A infection. His condition deteriorated as he developed adult respiratory distress syndrome (ARDS); during a stormy recovery exceptionally high doses of benzodiazepines and opiates were given in order to suppress voluntary breathing during a successful period of assisted ventilation. It is possible that benzodiazepine-opiate antagonism developed. Subsequent studies in laboratory mice indicate that the respiratory depressant effects of morphine can be antagonized by prior treatment with lorazepam.

Adolescent↗

PubMed1985

Plasma free captopril concentrations during short and long term treatment with oral captopril for heart failure.

Plasma free captopril concentrations and haemodynamic response to captopril were studied in 20 patients with severe chronic heart failure. A 25 mg oral dose of captopril produced a 36% reduction in systemic vascular resistance, with individual responses varying from 13% to 64%. Mean systemic pressure fell by 20% and cardiac output rose 28%. The absorption of captopril was rapid. Peak plasma free captopril concentration occurred at 45 minutes after the dose and was followed by a smaller second peak. Peak plasma free captopril concentrations varied more than 20-fold but did not correlate with the maximal reduction in systemic vascular resistance. Elimination half life was seven hours. Fourteen patients were restudied after 1-2 months of captopril treatment and 12 showed symptomatic benefit. There was a sustained improvement in haemodynamic state and in non-invasive indices of myocardial function. During long term treatment the predose plasma free captopril concentration correlated well with dosage, but steady state captopril concentrations did not show a significant relation with haemodynamic response. On a dosage regimen of 25-50 mg three times daily the morning predose plasma free captopril concentration and plasma renin activity were relatively low and suggested that maximal inhibition of the renin-angiotensin system was not maintained throughout the dosage interval.

Aged↗

PubMedDate not supplied

A new hereditary cylindromatosis family associated with CYLD1 on chromosome 16.

Hereditary cylindromatosis (HC; MIM 132700) is an autosomal dominant condition characterized by benign skin appendage tumors most commonly on the scalp and face. Previously, the HC gene (CYLD1) was linked to chromosome 16q12-13, and tumors showed loss of heterozygosity (LOH), suggesting that CYLD1 is a tumor suppressor gene. Here we report a new multi-generation cylindromatosis family whose condition maps to that region, with 7/13 tumors showing LOH on 16q.

Adult↗

PubMedDate not supplied

QSAR studies on P-glycoprotein-regulated multidrug resistance and on its reversal by phenothiazines.

Multidrug resistance is brought about largely by membrane transport proteins such as P-glycoprotein (P-gp). We have developed a quantitative structure-activity relationship (QSAR) for P-gp-associated ATPase activity for a diverse set of 22 drugs, and found that such activity is related to substrate molecular size and polarity. We have also developed a QSAR for drug efflux from the blood-brain barrier of another diverse set of 22 drugs, and found that such efflux is a function of drug size and polarisability. Thirdly, we have carried out a QSAR analysis of the ability of 157 phenothiazines and related drugs to reverse multidrug resistance. We were unable to obtain a good QSAR for the whole data-set, but when we divided the data-set into sub-sets of closely related structures, a series of good correlations was obtained, most of which incorporated descriptors that model molecular size and polarity/polarisability. In no instance did we find any evidence that hydrogen bonding or hydrophobicity play a part in multidrug resistance or its reversal, despite that fact that several other workers have reported that these effects appear to be important here.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMedDate not supplied

Quantitation of fluoride ion released sarin in red blood cell samples by gas chromatography-chemical ionization mass spectrometry using isotope dilution and large-volume injection.

A new method for measuring fluoride ion released isopropyl methylphosphonofluoridate (sarin, GB) in the red blood cell fraction was developed that utilizes an autoinjector, a large-volume injector port (LVI), positive ion ammonia chemical ionization detection in the SIM mode, and a deuterated stable isotope internal standard. This method was applied to red blood cell (RBC) and plasma ethyl acetate extracts from spiked human and animal whole blood samples and from whole blood of minipigs, guinea pigs, and rats exposed by whole-body sarin inhalation. Evidence of nerve agent exposure was detected in plasma and red blood cells at low levels of exposure. The linear method range of quantitation was 10-1000 pg on-column with a detection limit of approximately 2-pg on-column. In the course of method development, several conditions were optimized for the LVI, including type of injector insert, injection volume, initial temperature, pressure, and flow rate. RBC fractions had advantages over the plasma with respect to assessing nerve agent exposure using the fluoride ion method especially in samples with low serum butyrylcholinesterase activity.

Animals↗